Understanding Electromagnetic Pulse and How to Prevent Resulting Damage to Electrical Equipment

One of the many fables of nuclear war that has been worn out in an

effort to convince us all the futility of it all is EMP. When

understood, the problem can take on realistic proportions.

When a nuclear explosion occurs, a very broad spectrum of energy is

released. It ranges from nearly DC (o KHZ) to beyond 1021 hertz

(gamma rays). The portion concerned with here ranges from 0 KHZ to

1000 GHZ (beyond radar uses).

Two basic sorts of damage can occur as a result of EMP. The first being

what we will call " power line " type of damage, and the other being what

I'll call " radio " damage. Power line damage is resultant from the

induction of high levels of current into relatively long wires such as home

or shelter wiring, electrical generating system wiring such as the cables

running to and from PV ( photovoltaic ) panels, generators, windmills, and

of course in the already famous auto electronic ignition system. This type

of damage can be virtually eliminated by a multi-level approach, that

provides front line defenses, and various levels of backup systems in the

event that EMP should overcome the first level of defense. This layered

defense method has proven highly reliable in commercial communications

systems where radio towers are subject to severe direct lightning strikes.

Even with such severe EMP and direct surge conditions which exceed most

predicted EMP conditions, the communications systems survive often for

years of storm seasons.

The first layer of EMP defense is the THYZORB. This is a solid state single

junction device similar to an avalanche diode. Its maker is National

Semiconductor, and it is distributed by Square D. You should purchase these

devices specifically matched to the type of system voltage you wish to

protect. For instance, if you wish to protect a 12 VDC PV system, you

should consider that the open circuit voltage of most PV panels is around

19 VDC so a 25 VD C THYZORB would provide excellent protection. Also

remember that as the amount of current through the device increases, so

does the voltage drop across the device. Generally about 10 VDC is to be

expected at maximum rating, thus we can expect that no more than 35 VDC

will develop at the protected area.

I would place a Thyzorb on each panel at the output terminals and then one

more at the junction of the panels where your main feed line is connected.

The THYZORB is available in many power ratings from 1.5 KW to 15 KW.

Generally you should be safe with the small ones on the panels, and the 15

KW unit at the junction point. At the other end of the feedline add another

THYZORB just as the first one at the junction point was. The device only

has two connections on it which are placed directly across the lines to be

protected. Under normal conditions, the unit has no effect on the

circuitry. The unit is reliable and re-useable. After thousands of

operations, it will still be as good as new. The reaction time for those

who wonder about such things is about 10 nano seconds. In the event your

cables are longer than ten feet or so, it wouldn't hurt to add a THYZORB

every ten feet. THYZORBS are available in many voltages and in AC or DC.

This means you should be installing them in any AC lines such as inverter

outputs or generator outputs. I would put one in every wall outlet and

light fixture also. Now for the layered effect I mentioned earlier.

In the event the THYZORB fails you need to have another device in place to

soak up the balance of the surge. In low voltage DC systems your choices

are somewhat limited. You could use an MOV ( metal oxide varistor ). These

are devices made by General Electric. They are widely available at stores

like Radio Shack. The only problem with MOV's is that every time they fire

(see a surge) they drift in value a little. Pretty soon your surge stopper

isn't turning on at the right time or worse yet fails altogether. In low

voltage systems, you can't really use a gas discharge tube, since they only

work at 150 volts or higher. By then your low voltage equipment will be

fried. Instead, at the risk of sounding redundant, I recomend another

THYZORB but selected at a slightly higher voltage. Five volts higher would

be a good choice since the second one would only fire if the first one were

working at 1/2 of its full capacity. This would cause a current sharing

condition and increase overall device reliability. You could in theory go

several layers in this manner until you felt completely safe, or you ran

out of EMP money. The actual connections would be to earth ground the

negative (-) side of your DC power system in several locations. Use long

bronze, brass, or copper rods with heavy, short cables to the power system.

Next attach the negative (-) side of the protection device, ( THYZORB or

other ), to the ground system. Finally, attach the positive side of the

protection device to the positive side of the power system. In an AC

system, you can do exactly the same as above with proper device selection.

You may also use a gas discharge tube here since we are dealing with a high

voltage to start with. In this case you will have three wires to deal with;

one for each side of the AC, and one for earth ground. Additional

preventive measures include grounding the frame of the PV panel and

grounding generator frames. A good earth ground is very important if you

use gas discharge tubes. If scenes from the " DAY AFTER " have you paranoid

about being trapped in an immobile car, then take heart. You can EMP proof

your auto electrical system the same way as your low voltage DC system.

Just put a couple layers of THYZORBS or MOV's across the DC input to the

ignition system. A few more sprinkled here and there like the power wires

of your CB radio, or your AM/FM receiver will work wonders. An easy way to

reduce the risk of appliance damage in your home or shelter, if it is an AC

device is to use a personal computer style surge protector. They are cheap

and very easy to install. Most of these devices use MOV's or better yet

THYZORBS or avalanche diodes.

  Imagine a very bright flash in the sky! No one is hurt. But, your transistor

radio stops playing, your car won't start, the telephone doesn't ring,

lights stay off, and we find ourselves in the stone age!

THE development of modern high-tech semiconductor devices have paralleled

unsettled relations between the nations of the world with resulting technol-

ogical advances affecting the lives of every citizen of North America. Com-

munications have been made faster, automobiles more fuel-efficient and

maintenance-free, TV sets, video-tape recorders, and virtually every other

piece of electronics equipment have been improved by the advent of the

semiconductor and its high-tech advancements. The relationship between

nuclear weapons and the recent electronics advances may seem unclear, but

a nuclear attack on the North American continent could make that relationship

glaringly apparent.

ALL nuclear explosions produce electromagnetic pulses (EMP's) and the ensuing

induced voltages and currents produced in conductors ( wires and cables ) are

comparable in strength to the strongest of lightning bolts. EMP's may reach 3

million volts and 10,000 amperes for a total of 30-billion watts of energy.

The largest commercial radio stations in the U.S. and Canada radiate 50,000

watts, or approximately one-millionth that much power! The major difference

between EMP's and lightning is that EMP's are induced simultaneously over

an entire wide area, while lightning occurs at a single location.

Significance of the Problem

------------ -- --- -------

THREE ten-megaton thermonuclear weapons detonated 250 miles ( 400 kilometers )

above the United States or Canada would produce EMP's strong enough to knock

out the entire electrical power grid of North America including the entire

civilian-telephone network, and just about every broadcast station.

Virtually every piece of unprotected electronic equipment in the country

-- radios, TV sets, computers, electronic controls in homes, office buildings, factories, cars, airplanes, and instruments in hospitals -- would be

damaged, if not destroyed. The pulses would also damage or destroy large

portions of the military command's control and communication (C3) system.

A chain reaction could be set in motion at nuclear power plants, due to elec-

tromagnetic pulses. Although it is a point that is frequently disputed, the

possibility exists that reactor core meltdowns might occur as a result of

EMP's. The meltdowns would be a by-product of electronic control system

failure. The control systems are used to monitor and control the processes at

the plants. The EMP's could cause the system to fail and result in partial or

complete loss of control over vital functions, causing subsequent melt-

downs. We know that those nuclear plants are designed to be fail safe,

but has anyone considered the possibility of every circuit breaker in a

plant failing at the same instant?

Characteristics of EMP's

--------------- -- -----

AT an altitude of 250 miles, the gamma rays produced in the first few nano-

seconds ( billionths-of-a-second ) of a nuclear explosion can travel hundreds

of kilometers before colliding with electrons in atmospheric molecules.

That kind of collision may take place in a region 2,000 miles in diameter and

6-miles thick. Electrons are accelerated by those collisions, a phen-

omenon referred to as the Compton effect; and upon reaching the earth's

magnetic field, they set up electromagnetic pulses that radiate downward

toward earth (Fig.1). Due to the extremely large area of collision, vast

amounts of ground area are exposed to electromagnetic fields with strengths

up to 50,000-volts per meter. The ground area exposed to electromagnetic

pulses could cover the entire continental United States and most of

Canada by one nuclear blast; if not, certainly large regions such as New

England would be electrically and electronically devastated.

FIG. 1 -- Electrons set into motion by gamma rays from a nuclear explosion in

space will produce enormous electromotive pulses (EMP's) when the negative

charges enter the Earth's magnetic-field. It is estimated that the ideal

height for such an explosion should be 250 miles above the Earth's surface.

:::::::::::::::::::::::::::::::::::::::

: :

: O - Nuclear Explosion :

: :

: / / :

: / / - Gamma Rays :

: --------------------------- :

: < Earth's Magnetic Field > :

: --------------------------- :

: ******* ******* ******* :

: ***** ***** ***** :

: *** EMP *** EMP *** :

: ***** ***** ***** :

: ******* ******* ******* :

: =============================== :

: EARTH :

: :

:::::::::::::::::::::::::::::::::::::::

Vulnerability

-------------

THE effects that electromagnetic pulses would have on a mass of circuitry are

difficult to predict because the interactions are complex. But, the more

complex the components, the easier they are to damage. Power lines are one

avenue for EMP damage, and a company making a shielded tubing to go over

power and signal carrying conductors obviously had EMP in mind when they

invented their "Zippertubing". That covering acts as a partial shield

to EMP's.

FOR each component, damage would come from the internal pickup of the circuit

itself, as well as surges fed to it by all other attached conductors (power

lines, other circuits,and metal parts). ANOTHER concern is that generators and

motors with their numerous internal windings of copper wire could be

rendered useless in an EMP attack; and with subsequent inoperative water

pumping stations, desert population-centers could persih. In the dead of

winter, motors in heating units would be destroyed and the chilling freeze in

the northern portions of the North American continent would bring those

areas to a standstill. Food and fuel shipments would halt because fusible

links and electronic ignitions would be destroyed in cars and trucks. It's

difficult to conceive a family anywhere on the continent not suffering extreme

hardships.

THE more complex the electronics components, the more vulnerable they

are to electromagnetic pulses. Hardness describes the vulnerability of an

electrical device and it is best for old-style vacuum tubes, less for semi-

conductors, and even less for microcircuitry. It would take 100 times

more EMP energy to damage the tubes than integrated circuits. Computers

may be upset through memory erasure with 100 times less energy than

required to damage integrated circuits; refer to Fig. 3. Aircraft in the air

and parked on open surfaces would be disabled, because electronics controls

the crafts' flight instruments and control surfaces.

:::::::::::::::::::::::::::::::::::::::

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:( Powers of TEN) :

:::::::::::::::::::::::::::::::::::::::

: RANGE OF THRESHOLD ENERGY, JOULES :

:::::::::::::::::::::::::::::::::::::::

: # = Motors and Transformers :

: $ = Vacuum Tubes :

: % = Low-Power Transistors :

: & = Integrated Circuits :

:::::::::::::::::::::::::::::::::::::::

Hardening Communications Equipment

--------- -------------- ---------

HARDENING of electronics communications equipment is vital to the military,

and, to a lesser extent, the civilian populace. The Department of Defense

has established an Electromagnetic Compatibility Program (EMCP) to ensure

that all military Communication-Electronic (CE) equipment subsystems, and

systems are protected from electromagnetic interference of all kinds.

That program was implemented to ensure that electromagnetic compatibility is

maintained through design, acquistion, and operational phases. Numerous semi-

conductor manufacturers now produce what are called "radiation-hardened"

integrated circuits, just for that reason.

THERE are three major design criteria which must be considered when hardening

against EMP's. They are cost, the equipment's ability to survive EMP, and

failure rates of the shielding components.

COST includes both installation and maintenance. Some protection practices,

such as shielding the entire communication site, may be attractive from a

technical point of view, but are impractically expensive.

THE electronic equipment's ability to survive an EMP attack must be measured

in order to determine how much EMP protection is needed. A testing device

for measuring the radiated electromagnetic susceptibility of an elect-

ronic device is a Transverse Electromagnetic Mode (TEM) cell. A TEM cell

consists of a group of electronic instruments and a special specimen holder

that simulates an environment of free space. The TEM cell is used for per-

forming electromagnetic interference/electromagnetic compatibility (EMI/EMC)

measurements and evaluating protection devices.

Shielding Methods

--------- -------

IN order to predict the effect of an electromagnetic pulse on electronic

equipment, it is necessary to assess the enviroment. The structures housing

the electronic equipment are made in various shapes and sizes, and are con-

nected to the outside world by conductors such as utility lines and pipes,

communication lines, and access and ventilation structures.(Refer to fig.5)

That combination of criteria makes the exact determination of the interaction

of an EMP with such a variety of structures extremely difficult. However,

for complex systems, it is convenient to have several layers of shielding.

(Refer to Fig. 6).

:::::::::::::::::::::::::::::::::::::::

: EMP Lightning :

: //// V V V :

: ------------------------------ :

: !* Building ! :

:P--+** ! :

: !* ! :

: ! EMP Penetration ! :

: ! ! :

: ! ! :

: +-+ * ! :

: ! ! *** ! :

: ! -----!------------------------ :

: ! ! :

:=!======!========================== :

:Gnd ! - Buried Cable :

:--------+ :

:::::::::::::::::::::::::::::::::::::::

: P = Power Lines Fig. 5. -- :

: -- A sealed metal box is an ideal :

: structure for eliminating EMP pen- :

: etration. However, power lines and :

: signal cables require entry ports :

: thus compromising the integrity of :

: a shielded building. Obviously, it :

: is apparent that doors and windows :

: would have a greater leakage effect.:

:::::::::::::::::::::::::::::::::::::::

: Shield 1 :

: ******************** :

: * Zone 1 (internal) * :

: * ============== * :

: * = Zone 2 =----* :

: * g = ########## = g * :

: * r = ############ = r * :

: * o =--###ZONE 3### = o * :

: * u = ############--= u * :

: * n = ########## = n * :

: * d = (cabinet- = d * :

: *---= environment) = * :

: * ============== * :

: * Shield 2 * :

: ****************** :

: !------! :

: ! :

: ! Zone 0 (External- :

: ! Environment) :

:----!--------------------------------:

: = EARTH :

: :

:::::::::::::::::::::::::::::::::::::::

: Fig. 6 -- More than one shield can :

: be used to secure the environment of:

: the machinery and electronic mat- :

: erial contained within a building. :

: The building can provide the initial:

: shield. Shielded rooms or metal cab-:

: inets may provide a second shield. :

: A third shield (not diagrammed) :

: would protect entry cables from :

: violating the shielded area of :

: zone 3. :

:::::::::::::::::::::::::::::::::::::::

Shield 1

------ -

A structure composed of a great deal of metal is well shielded against electro-

magnetic pulses, while a building made primarily of wood is virtually un-

shielded against EMP's. Continuous, closed sheet-metal shields are, by far,

the most effective electromagnetic shields. It is imperative that the in-

ternal environment of zone 1 be connected to the outside world. That fact

makes a closed sheet-metal shield impossible. Aperatures in shield 1

create a special problem in protecting communication sites from EMP penetra-

tion.

THE electromagnetic field penetration depends on the aperature size. If a

given area of wall opening is subdivided into ten small openings having

the same total area, the penetrating EMP fields at an interior point will be

1/SQR(10) as large as for a single large opening of the same total area.

(Refer to Fig. 7).

Therefore, it is better for a structure to have more small openings than

just a few larger openings.

A common treatment for such openings is to cover them with a conducting

screen or mesh so that the large opening is converted to a multitude of

small openings, or use a glass impregnated with metal. That glass, despite

having metal in it, offers approximately the same degree of visual att-

enuation or lack of clarity as looking through a screen door from within the

house.

:::::::::::::::::::::::::::::::::::::::

: !! !! :

: ###### !! ######## !! :

: # !! # !! :

: EMP *==!! # !! :

: # !! # !! :

: # !! E *==!! :

: EMP *==!! M **==!! :

: # !! P **==!! :

: # !! *==!! :

: EMP *==!! # !! :

: # !! # !! :

: # !! # !! :

: EMP *==!! # !! :

: # !! # !! :

: # # :

: ###### ######## :

: Shield Shield :

:::::::::::::::::::::::::::::::::::::::

: Fig. 7 -- The electromagnetic field :

: penetration into a ported shield is :

: minimized by reducing the size of :

: the openings. In the diagram the :

: open area of the port of the example:

: on the right is equal to the sum of :

: the areas in the example at left. :

: The diagram clearly shows that the :

: penetration of an EMP is less when :

: equal areas are summed from several :

: small ports. :

:::::::::::::::::::::::::::::::::::::::

Shields 2 and 3

------- - --- -

THE second-level shield seperates the internal environment from the sensitive

small-signal circuits within the electronic equipment found within Zone 2.

Shielding here may be accomplished by electrically grounding the metal cabin-

ets and equipment.

SHIELD 3 involves the shielding of the interconnection of the equipment. That

could involve elaborate design of interconnecting signal transmission lines.

Fiberoptic signal transmission shows great promise here because it is

not effected by any type of electromagnetic interference.

Hardening Aircraft and Missles

--------- -------- --- -------

GENERALLY, the EMP interaction with electrical systems inside structures such

as aircraft and missles depends upon a multitude of factors. Aircraft and

missles usually have a nearly complete metallic exterior covering that serves

as a shield from electromagnetic fields. However, that shield alone is

not enough protection against electromagnetic pulses.

Missles and Aircraft are equipped with computers that cannot be upset even for

an instant. They must be partically well hardened.

AT the present time, there is no agreement on the most effective ways to

harden aircraft and missles. Heavy shielding, like the type used at com-

munication sites, is obviously impractical because of the added weight that

the aircraft has to carry. Instead, EMP resistance is designed into the

aircraft's equipment. One example of that would be in the area of circuit

design. Small loops make better antennas for EMP's than short straight

lines; therefore, circuits are designed in tree or branching layouts rather

than in more conventional circuit loops.

Is Shielding Help on the Way?

-- --------- ---- -- --- ----

IN the last decade, electronic devices have proliferated in all areas of our

lives. That influx of products has caused a problem: Noise Pollution, or

EMI/RFI ( electromagnetic/radio frequency interference). Over 80,000 cases

of noise pollution were reported to the FCC (Federal Communications Commission)

in 1982.

STRANGE as it may sound, the plastics industry is coming to the rescue with

plastic electronic-equipment enclosures specifically designed for both EMI con-

tainment and shielding. Obviously, with EMP's as an external disturbance, the

containment of a field is academic, but the shielding from an outside field is

crucial. The parameter describing that is Shielding Effectiveness (SE) and the

equation for shielding effectiveness is

SE = A + R,

or shielding effectiveness equals Absorbed plus Reflected energy.

HIGHLY conductive materials such as pure metal shields reflect approximately 99

percent of the energy and adsorb 1 percent. But plastics with metallic comp-

osite fillers, metallic paints and sprays, or even impregnated wire meshes

still reflect 80 percent of the energy and absorb 20 percent. If EMP's and the

disturbing effects of electromagnetic fields still seem like an abstraction or

a physicist's dream, consider that event.

A manufacturer of buses designed for city use had just delivered a fleet when,

during a test drive, a problem was discovered. After going over the top of a

hill, the driver tried to brake, only to discover he had no brakes until he got

to the bottom of the hill. Upon logical investigation of that problem, field-

strength meters demonstrated that a local television station had a lobe-shaped

radiation pattern that intersected the hill's apex. The microprocessor-

controlled anti-skid braking system on the bus had sensitive circuitry that

became inoperative because of the TV signal. The bus, though, was made safe

by properly shielding the enclosure housing the electronics. Graphite,

a moderately good conductor, is fabricated within large plastic sheets

for applications such as that.

IF a signal as small as that can effect circuitry that drastically, you can

imagine what an EMP could do and likewise you can see how crucial EMI

shielding is. But will EMI shielding be universally implemented into new

equipment?

The Military's Involvement

--- ---------- -----------

THE military is very concerned with EMP's. The Army has established its

Aurora Tree test facility in Aldelphi, Maryland. The Navy has the Casino and

Gamble-2 x-ray emitting facilities, but the Air Force probably has the most

interesting project of all. It is the Trestle, after the railroad structure

it resembles.

THAT 12-story (118 feet) high, 58-meter (200-foot) square deck is flanked by a

50-foot wide adjoining ramp upon which aircraft to be tested are rolled up.

The Trestle can support aircraft weighing 550,000 pounds and is built

with one-foot by one-foot wooden columns using no nails or metal of any

kind. That largest glue-laminated structure in the world uses 250,000

wooden bolts to hold its six-million board feet of lumber together ---

enough for 4,000 frame houses. The structure at Kirtland Air Force Base,

New Mexico cost approximately 58-million dollars.

THE Trestle has two 5-million volt pulsers that discharge energy into

wire transmission lines surrounding the aircraft under test. Sensors

capture aircraft response signals and fiber-optic channels transmit

that sensor data to computers for processing. The processing equip-

ment, though, naturally resides inside a very well shielded structure.

The B-52G's OAS (Offensive Avionics System) is one of numerous studies

directed primarily at testing the electronic hardening of military

systems.

The Future

--- ------

THE effects of EMP on our lives is becoming known to many on the North

American continent as it is being discovered by all the citizens of

the free world. Its political implications are not the topic here,

but rather the facts in this article reveal to what EMP is and what it

can do to the technological devices we rely on every minute of the day.

The next time a solar flare disrupts radio communications around the world

for a few hours, or maybe a few days, recall that man with one nuclear

device can outshine the damage old Sol creates by many fold.

GLOSSARY OF TERMS

-----------------

ElectroMagnetic Pulse (EMP): An electromagnetic field of high

intensity and short duration that may be caused by a nuclear

explosion.

-----------------------------------

Electromagnetic Field: A magnetic field produced by elect-

ricity (the flow of current in a wire or electrons through a medium

such as a vacuum). It is usually expressed in volts per meter.

-----------------------------------

ElectroMagnetic Compatibility (EMC): The ability of an electronic device

to deal with electromagnetic interference and function properly.

-----------------------------------

ElectroMagnetic Interference (EMI): Any adverse effect on electronic

equipment due to an electromagnetic field.

-----------------------------------

Shielding or Hardening: A method used to protect electronic devices

from EMP interruption or damage.

-----------------------------------